Loss separation of amorphous and nanocrystalline Fe85−xCoxNb7B8 alloys in weak magnetic field at low frequency

The three types of losses of amorphous and nanocrystalline Fe85 − xCoxNb7B8 (x = 2, 5, 10) alloys are analyzed through Legg equation. The ratio of each type of loss changes with the composition. For the as-melt spun state, the hysteresis loss is dominant and the eddy current loss is negligible. After nanocrystallization by thermal treatment, the ratio of each type of loss has changed due to the formation of the composite microstructure of embedded nanoscaled α-FeCo grains in amorphous matrix. The eddy current loss is no longer small because the conductivity is enhanced by nanocrystallization. With the improvement of magnetic properties, the magnetic hysteresis loss in nanocrystalline alloys decreases as compared with that in the amorphous state. The excess loss in thermal treated samples increases greatly with the increase of cobalt content because the homogeneous amorphous structure is disassembled after thermal treatment.